The subject invention relates to an improved method for cleaning the elements of a rotary valve regenerative oxidizer. More specifically, the subject invention relates to a method for continuously cleaning the elements of rotary valve regenerative oxidizer while on-line.
Regenerative oxidizes are used to remove contaminated gas, such as volatile or condensable and particulate organic compounds from an air stream. The contaminated gas is typically generated from an industrial process such as, for example a paint application or bake process in an automotive paint shop, and the wood industry, grain industry, etc. Two types of regenerative oxidizers are commonly used, a thermal oxidizer, and a catalytic oxidizer. The regenerative thermal oxidizer removes contaminated gas by a combustion reaction. To remove the contaminated gas, the combustion reaction must reach a temperature that breaks down the volatile organic compounds to corresponding CO.sub.2 and H.sub.2 O. The catalytic oxidizer removes the contaminated gas by a catalyzed reaction that is typically an exothermic reaction. This is achieved by accelerating the oxidation process of volatile organic compounds with precious metals on a ceramic substrate.
Referring to a thermal oxidizer, which is more widely used than a catalytic oxidizer, the contaminated gas is passed through a first heat exchange chamber having a media disposed therein. The media is preheated to a combustion temperature to facilitate the combustion reaction as the gas contacts the media. The heated and purified gas passes through a single or a plurality of first heat exchange chambers into a combustion chamber. The combustion chamber includes a flame source that only operates when heat is required to be added to the process, which is typically only during a start-up period. The heated and purified gas passes through the combustion chamber and into a second heat exchange chamber having media disposed therein and subsequently out of the oxidizer through an outlet stack. As the process continues the first heat exchange chamber will become fouled with organic solids that can build up to a level of becoming a potential source for fire.
As disclosed in U.S. Pat. No. 5,538,420 to Klobucar et al, to operate the oxidizer continuously, a third heat exchange chamber is added to the process. The third heat exchange chamber receives purge gas drawn from ambient air that has been passed through a heater element for heating the gas to a temperature that will clean volatilized organic solids from the media and walls of heat exchange chamber. The purge gas pass into the combustion chamber, and subsequently out through the second heat exchanger. The purge gas originates as ambient air and is heated from ambient air temperature to the cleaning temperature. The Klobucar et al patent discloses three independent chambers each having an inlet valve, an outlet valve, and a purge valve. The valves cycle during operation so that one chamber is operating as in inlet chamber for heating and purifying the gasses, one chamber is operating as an outlet chamber, and one chamber is being cleaned.
The Klobucar et al patent provides the ability to operate the regenerative oxidizer continuously. However, the valves required for continuous operation are complex and costly. In addition, heating ambient air to a temperature high enough to clean organic solids from the heat exchange chambers is not energy efficient and adds to the operating costs. The valve design also prevents rapid rotation of heat exchange chambers to the cleaning stage of the process.
An alternative embodiment is disclosed in English Patent no. 791,222. The invention, as disclosed in this patent, replaces the three valves disclosed in the Klobucar et al patent with a rotary valve. The rotary valve includes an inlet section, an outlet section, and a purge section, each aligned with pie shaped heat exchange chambers that are arranged in a circular fashion. The rotary valve pivots about a tubular member 40 for alternating the chambers that align with the various valve sections. Cleaning vapors are directed into the tubular member and through the purge section for cleaning volatilized solids from the heat exchange chambers.
The English '222 patent discloses a more simplified structure by replacing the valves, as disclosed in the Klobucar et al patent, with a rotary valve. It does not, however, disclose a method for reducing the energy requirements associated with cleaning the various heat exchange chambers.
Therefore, a need exists for a method of continuously cleaning the heat exchangers in a regenerative oxidizer at a rapid rate, and in an energy and cost efficient manner.